Distance measuring equipment (DME) is a transponder based radio technology that measures distance by timing the propagation delay of radio signals. Aircraft use DME to determine their distance from a land-based transponder by sending and receiving two pulses of fixed duration and separation (pulse pairs).
An aircraft communicates with a ground transponder using a series of pulse pairs (interrogations) and, after a precise time delay (50 microseconds for Mode X or 56 microseconds for Mode Y), the ground station relies with a pulse pair with the correct spacing. The DME receiver in the aircraft searches for pulse-pairs with the correct time spacing (12 microseconds for Mode X and 30 microseconds for Mode Y).
Aircraft have several independent radios. Integrating the various L-Band radios on an aircraft would reduce the size, weight, power and cost of the radios. However, DME transmitters are typically implemented using a saturated Class C amplifier with a drain modulator; integrating DME transmitters with other L-Band radios would be difficult to achieve using a saturated Class C amplifier with drain modulation transmitter architecture. Furthermore, some implementations of integrated L-Band radios may require extensive calibration under various operating conditions. extensive calibration may be prohibitive.
Consequently, it would be advantageous if a method and apparatus existed that are suitable for integrating various L-band radios into a single self-calibrating radio architecture.